This invention relates generally to a printing press and more particularly to a mounting arrangement for a plate cylinder and associated form rollers.
In a web press or a sheet-fed press, the printing work is performed by applying ink from an ink fountain to a printing plate on a plate cylinder by means of ink form rollers through vibrating rollers and so forth, then transferring the ink onto the surface of a rubber blanket roller rotating in pressure contact with the plate cylinder, and further transferring the ink onto a web or sheet passing through the blanket roller. In such printing work, the contact pressure of the ink form rollers against the plate cylinder is an important factor and should be adjusted uniformly in the longitudinal direction with high accuracy.
FIG. 1 shows schematically the position of a plate cylinder in a conventional rotary press. Vibrating rollers 4 and a plate cylinder 1 are journalled in a pair of spaced frames and form rollers 3 are disposed in rolling contact with the plate cylinder 1 and the vibrating rollers 4. A supporting shaft 6 for each of the form rollers 3 is rotatably supported at either end by eccentric sleeves 5 received in bores of a pair of roller holders 2 which are swingably mounted on a shaft 7 of its associated vibrating roller 4. Thus, by rotating each eccentric sleeve 5, the distance between the axes of the respective form rollers 3 and the associated vibrating rollers 4 can be changed. An adjustable biasing means 8 is attached to each of the roller holders 2 for urging the form roller 3 in contact with the plate cylinder 1.
In this structure, control of the contact pressure of the respective form rollers 3 against the plate cylinder 1 is performed by first rotating the eccentric sleeves 5 to adjust the pressure between each form roller 3 and the vibrating roller 4, and then operating the biasing means 8 to adjust the pressure between the form roller 3 and the plate cylinder 1. The pressure adjustment in such conventional arrangement is, however, very difficult to make and requires much time because the adjusting operation has to be performed manually among multiple rollers.
For precise registration of impressions, skewing adjustment of the plate cylinder is often conducted. To achieve this purpose, one end of the plate cylinder is supported by an eccentric sleeve rotatably mounted in the frame. A rod is connected to the eccentric sleeve and the skewing adjustment is executed by rotating the eccentric sleeve by means of the rod. Smooth adjustment of the rod becomes, however, difficult where the plate cylinder is arranged to be displaced axially for lateral adjustment. Moreover, with the arrangement shown in FIG. 1, the uniformity of the contact pressure between respective form rollers and the plate cylinder is lost after the skewing adjustment.
For interrupting application of the ink onto the printing plate, a roller throw-off mechanism is used. For example, in the arrangement shown in FIG. 1, the throw-off is achieved by rotating an arm 9 by an air cylinder (not shown) in the direction of the arrow so as to separate the form rollers 3 from the plate cylinder 1 by way of a cam 10, a cam lever 11, a connecting rod 12 and a roller lift lever 13. With respect to the purpose of changing the distance between the axes of the form roller 3 and the plate cylinder 1, both the roller lifting action and the contact pressure adjustment can be regarded as the same, and therefore it is desirable that these two actions are performed by a single mechanism.